In vehicular network environment, various applications achieve an interchange between vehicular states and events through periodic messages, such as road hazard signaling (RHS), intersection collision risk warning (ICRW), signal violation warning (SVW), transit signal priority (TSP), pre-crash warning (PCW), etc., which are common applications in vehicular network environment.
When the periodic messages of these applications are performed in the same environment, serious channel congestion problems may take place, thereby impacting the immediacy of important messages, especially for security messages. Regarding this issue, international associations such as European Telecommunications Standards Institute (ETSI)|[Andy Jengl], begin to establish standards to set up a series of standards for decentralized congestion control (DCC). Current standards and techniques mainly consider the characteristics of mid-lower levels (network and transport level and access level) such as channel quality, without considering a facility level for the information provided by an application level. In other words, currently the minimum interval of messages being generated is determined based on channel load and message types (degree of priority), that is, to predetermine the transmission interval for various message types, degree of priority thereof, and various messages in different conditions. In practice, appropriate transmission intervals can be selected as the generation frequency of messages based on current channel load degree. Although this approach prevents low-priority messages from overly occupying the channel, emergency message frequency is inevitably limited. Accordingly, it is not ensured that the required generation frequency of the emergency messages with high priority is met. Therefore, the emergency messages with high priority are not immediately transmitted, and the latency reduces the driver's reaction time, which even causes danger.
Thus, there is still room of improvement for the generation frequency of messages, especially for preventing low-priority messages from overly occupying channels while satisfying the generation frequency of emergency messages with high priority.